1. Field of the Invention
The invention relates to a continuous-flow heater for molten metal, for instance, an induction crucible furnace for maintaining or increasing the temperature level of a metal melt.
2. Description of the Prior Art
In metallurgy it is often necessary to bring large quantities of a molten metal from one temperature level to a higher temperature level or, if the melted amount of metal cannot be poured immediately, to maintain the temperature level of the molten metal. This can take place either in batch operation or continuously in a continuous-flow heater. In principle, any known electrically heated melting furnace can be used for this purpose.
If an arc furnace is used for heating the metal melt in batches, it must be noted however that the efficiency of the arc furnace for this type of operation is very low and that reactions on the melt to be heated can occur. At the base of the arc furnace, very high temperatures occur which can lead to the evaporation of the melt and therefore of the alloy elements and can promote the absorption of nitrogen into the melt. If graphite electrodes are used, the melt, in addition, can absorb carbon.
While arc furnaces can be used for batch-wise heating, induction channel furnaces are available for continuous flow operation. Batch-wise operation with an induction channel furnace, on the other hand, is difficult for larger units and outputs because the temperature variations connected therewith, in particular in the refractory lining of the inductors, lead to considerable problems. Accordingly, changes in alloys and grade require a considerable expenditure of technical means.
To avoid the disadvantages of the arc furnace and the induction channel furnace, the induction crucible furnace--a furnace in which the crucible is heated from outside by electrically induced currents--has been used for batch-wise heating. Also special designs of induction crucible furnaces have already been used for heating in continuous flow operation. A tube with refractory lining which was provided for feeding-in the melt to be heated was brought through the rocker bearing of the induction crucible furnace. The discharge took place via a spout which was open or designed as a syphon, by tilting the induction crucible furnace. In another induction crucible furnace, the melt is fed-in through a slot provided in the lid. In both embodiments it was necessary to replace the crucible at shorter intervals than in normal induction crucible furnaces. Considerable war occurred mostly in the region of the crucible wall.